Masking device



April 25, 1967 T. J. HAJDUK ETAL 3,315,638

MASKING DEVICE Filed March 29, 1965 l Thuddeurs J. Hojduk Raymond J. Pekosh By 9,1/ i l A'rorney United States Patent O 3,315,638 MASKING DEVICE Thaddeus J. Hajduk and Raymond J. Pekosh, Chicago, Ill., assignors to The Rauland Corporation, Chicago, Ill., a corporation of Illinois Filed Mar. 29, 1965, Ser. No. 443,358 Claims. (Cl. 118-505) This invention relates to the manufacture of cathoderay tubes and more particularly to the provision of novel -apparatus for use in the application of a conductive coating to the interior surface of a cathode-ray tube envelope.

In the manufacture of conventional tri-color cathoderay tubes for use in color television receivers and the like, the envelope is composed of a screen panel section and a funnel section, both of glass, which are frit-sealed together at an appropriate stage in the manufacturing process. It is necessary in finished tubes to have a conductive internal wall coating on the inner surface of the funnel section of the envelope to serve as a final anode. The final anode coating is operated at the same potential as the aperture mask and the conventionally provided aluminum backing layer for the fluorescent screen, and accordingly it is conventional practice to provide snubber springs on the mask which are adapted to contact both the aluminum backing layer and the internal final anode coating. For optimum operation, and to minimize the length of the required snubber contact springs, the nal anode coating should extend very close to the open end of the funnel section of the envelope.

The final anode coating is conventionally formed of a suspension of colloidal graphite known as aquadag. While this material may be swabbed or brushed onto the inner surface of the funnel section of the envelope, it is preferred to spray the colloidal graphite suspension in order to assure maximum uniformity of the coating. Masking elements of various types have been employed to provide a sharply defined forward edge for the coating, but upon withdrawal of the masking elements there has been a definite tendency of the still wet coating suspension to smear. Moreover, it has been found that unless the masking element is cleaned after each use, considerable diiiculty has been encountered with smearing of the suspension onto the sealing edge of subsequently coated funnel sections. Unless this sealing edge is clean at the time it is juxtaposed with the screen panel section, the resulting frit seal is defective. Alternatively, the mask may of course be retained in place until the coating suspension has dried, but this is unduly time-consuming and not compatible with mass production assembly line techniques.

It is a principal object of the present invention to provide a new and improved apparatus for use in the application of a coating to the interior frusto-conical surface of the cathode-ray tube envelope.

A more specific object of the invention is to provide a new and improved masking apparatus for use in spray coating the inner wall of the funnel section of a tri-color cathode-ray tube envelope to assure a sharply defined boundary for the finished coating, while avoiding smearing when the fixture is withdravim.

Still another object of the invention is to provide such a new and improved masking apparatus which is simple and convenient to operate, which does not require cleaning after each use, which is adaptable to eccentric funnels or funnel dimensions of varying tolerances due to glass manufacture and which is readily adaptable to mass production assembly line techniques in the manufacture of tri-color cathode-ray tubes.

In accordance with the invention, apparatus for use in the application 0f a conductive coating to the interior ice surface of a cathode-ray tube envelope comprises a ring gasket of resilient material having leading and trailing edges and adapted for contacting the envelope surface throughout a predetermined circumferential area thereof. Means are provided for compressing the gasket against the surface throughout the predetermined contact area with a greater pressure at the leading edge than at the trailing edge.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE l is a perspective view showing the masking apparatus of the present invention as applied to the funnel section of a tri-color cathode-ray tube envelope during the spray application of an internal wall coating;

FIGURE 2 is a fragmentary cross-sectional view taken along the line 2 2 of FIGURE 1; showing the masking apparatus of the invention in engagement with the funnel section of the envelope during and immediately following the application of the spray coating; and

FIGURE 3 is a fragmentary cross-sectional view similar to that of FIGURE 2, illustrating withdrawal of the masking fixture from the cathode-ray tube envelope section after completion of the spray coating operation.

In FIGURE l, the funnel section 10 of a tri-color picture tube envelope is supported with its longitudinal axis 11 vertically oriented and the large end or cone upwardly directed, by resting on a support frame 12. A mask element 13 of rubber or other resilient material, to be described in detail, is supported by a pair of separate frame members 14 and 1S, the former being provided with indexing studs 16 which rest on the forward sealing surface 17 of the funnel section 10. The upper frame member 15 is keyed to lower frame member 14 in a manner to be described and is provided with a pair of handles 18 by which the entire masking fixture may be vertically withdrawn. When the masking fixture is in use, the resilient ring member or gasket 13 contacts the inner surface of the tapered portion of funnel section 10 as shown, and the colloidal graphite or aquadag suspension is applied, preferably by spraying as schematically illustrated by the showing of a conventional spray gun 19, to provide a conductive final anode coating 20 on the inner surface of envelope section 10.

The construction of the resilient ring member 13 is best visualized from a consideration of FIGURES 2 and 3. Ring member 13 is of a bifuracted construction, comprising a bight portion 21 having a tapered masking surface 22 with a leading edge 23 of smaller diameter than its trailing edge 2 4 and adapted to contact or mate with the inner surface of envelope section 10 throughout a circumferential area of a width corresponding to that of masking surface 22. The bifurcated ringmember v13 further comprises first and second divergent leg portions 25 and 26 respectively extending from theleading and trailing edges 23 and 24 respectively. Leg portions 25 and 26 each extends from bight portion 21 at an acute angle relative -to frusto-conical masking surface 24, generally in a paraxial direction relative to axis4 11 of the envelope section 10.

The outermost extremity of the outer leg portion 26 is aliixed to frame member l14, while the outermost extremity of inner leg portion 25, which is longer than outer leg portion 26, is affixed rto frame member 15. Frame member 15 is keyed to frame member 14 by a plurality of slide bolts 27, of which one is visible in FIGURES 2 and 3, the upper frame member v15 being countersunk below the heads of bolts 27 to permit paraxial motion of frame member 15 relative to frame member 14 when the masking fixture is withdrawn.

When lthe masking fixture is applied to funnel section of the envelope, as shown in FIGURE 2, frame member .14 is supported at a fixed distance above the rim of the funnel section 10 by the indexing studs 16 which rest on sealing edge 17. Frame member rests on frame member 14 in keyed paraxial alignment therewith. Leg portions and 26 of ring gasket 13 are proportioned to provide substantially greater buckling or deformation of the inner leg portion 25 than of the outer leg portion 26 when the masking fixture is in place. Thus, the masking surface 22 of the bight portion of ring gasket 13 is pressed outwardly into engagement wi-th the inner Wall of funnel member l10, with a greater contact pressure at leading edge 23 than at trailing edge 24, as a result of the greater stress in leg portion 25 than in leg portion 26.

When the masking fixture is withdrawn after spraying of the c-olloidal graphite coating 20, by lifting handles 18, frame .member 15 is independently raised to the extent permitted by the countersunk recesses in which the heads of slide bolts 27 are received, as shown in FIG- URE 3. Ring gasket 13 is so proportioned that at this point in the withdrawal of the masking fixture, the entire masking surface 22 of bight portion 21 remains in contact with the inner wall of the envelope section 10. With further lifting of the masking fixture .of handles 18, frame member 14 is raised along with frame member 115, and the trailing edge 24 of the masking surface of the resilient ring gasket 13 is withdrawn from contact with the envelope surface in advance of withdrawal of the leading edge 23, as clearly visible in FIGURE 3. With still further withdrawal of ythe masking fixture, the leading edge 23 is withdrawn from contact with the envelope surface, swinging inwardly :toward the axis 11 as it pivots about the fulcurm provided by the anchoring of leg portion 26 to frame member 14, this fulcrum being closer Ito axis 1.1 than the envelope surface engaged by masking surface 22 -of ring gasket y13. After ring gasket 13 swings inwardly clear of envelope section 10, it is paraxially withdrawn and is available for use in coating the next envelope section on the assembly line. Thus, even though the colloidal graphite coating is still wet, there is no tendency to smear, and the coating is left with a sharply defined forward edge. Moreover, since ring gasket 13 is maintained in contact with the inner surface of envelope section 10 with a greater contact pressure at the leading edge 23 than at the trailing edge 24, and since leading edge 23 is 4the last portion of the gasket to leave contact with envelope section .10, the masking surface 22 of the gasket is kept clean of the aquadag Suspension and the masking .fixture may be used repeatedly without the necessity -of frequent cleaning, .and there is no tendency to deposit unwanted graphite particles on the sealing edge 17 of subsequently coacted envelope sections.

Thus the invention provides a new and improved apparatus for use in the .application of a final anode coating to the inner surface .of a cathode-ray tube envelope. 'The apparatus is simple both in construction and in use, is superior to prior masking fixtures in avoiding unwanted vsmearing and contamination of the sealing edge, and is readily adapted to use in the mass production of color television picture tubes. While the illustrated embodiment is specifically designed for use in conjunction with a round screen tri-color tube, it is readily apparent that a similar construction may be employed in the application of a sprayed final anode coating in a rectangular color tube, the peripheral contour -of ring gasket 13 being shaped to correspond with that of the funnel section of the envelope of the particular tube to be manufactured.

While a particular embodiment of the invention has been shown and described, it will be. obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. Apparatus for use in the application of a conductive coating to the interior surface of a cathode-ray tube envelope comprising:

a bifurcated member of resilient material comprising a pair of divergent leg portions connected by a bight portion having leading and trailing edges and adapted for contacting said surface throughout a predetermined area thereof;

and means for applying said bight portion to said surface while differentially stressing said leg portions to compress said bight portion against said surface throughout said predetermined area with a greater contact pressure at said leading edge than at said trailing edge.

2. Apparatus for use in the application of a conductive final anode coating to the interior surface of a cathoderay tube envelope comprising:

a bifurcated ring member of resilient material comprising a bight portion having a frusto-conical masking surface with a leading edge of smaller diameter than its trailing edge and adapted for contacting said envelope surface throughout a predetermined circumferential area thereof, and further comprising first and second divergent leg portions extending from said leading and trailing edges respectively and each extending from said bight portion at an acute angle relative to said frusto-conical masking surface;

and means coupled to the extremities of said leg portions for applying said ring member to said interior surface of said envelope while stressing said first leg portion to a greater extent than said second leg portion to compress said masking surface of said bight portion against said interior surface of said envelope throughout said predetermined circumferential area with a greater contact pressure at said leading edge than at said trailing edge.

3. Apparatus for use in the application of a conductive final anode coating t-o the interior surface of a cathode-ray tube envelope comprising:

a bifurcated ring member of resilient material comprising a bight portion having a frusto-con-ical masking surface with a leading edge of smaller diameter than its trailing edge and adaptedv for contacting said envelope surface throughout a predetermined circumferential area thereof, and further comprising first and second divergent leg portions extending from said leading and trailing edges respectively and each extending from said bight portion at an acute angle relative to said fnisto-conical masking surface, said first leg portion being longer than said second leg portion;

and means coupled to the extremities of said leg portions for applying said ring member to said interior surface lof said envelope to compress said masking surface of said bight portion against said interior surface of said envelope throughout said predetermined circumferential area with a greater contact pressure at said leading edge than at said trailing edge, and for withdrawing said trailing edge in advance of said leading edge after the application of said coating.

4. Apparatus for use in the application of a conductive final anode coating to the interior tapered surface of a cathode-ray tube envelope having a predetermined longitudinal axis, said apparatus comprising:

a bifurcated ring member of resilient material cornprising a bight portion having a tapered masking surface with a leading edge of smaller diameter than its trailing edge and adapted for contacting said envelope surface throughout a predetermined circumferential area thereof, and further comprising first and second divergent leg portions extending from said leading and trailing edges respectively and each extending from said bight portion at an acute angle relative to said frusto-conical masking surface, said first leg portion .being longer than said second leg porti-on and closer to said axis;

and means comprising separate members respectively coupled to .the extremities of said legr portions for applying said ring member to said interior surface of said envelope while paraxially stressing said first and second leg portions to compress said masking surface of said bight portion against said interior surface of said envelope throughout said predetermined circumferential area with a greater contact pressure at said leading edge than at said trailing edge.

5. Apparatus for use in the application of a conductive nal anode coating to an interior tapered surface of cathode-ray tube envelopes each having a predetermined longitudinal axis, said surface having a different distance from said axis in a different envelope, said apparatus comprising:

a bifurcated ring member of resilient material comprising a bight portion having a tapered masking surface with a leading edge of smaller diameter than its trailing edge and adapted for contacting said envelope surface throughout a predetermined circumferential area thereof, and further comprising lirst and second divergent leg portions extending from said leading and trailing edges respectively and each extending from said bight portion at an acute angle relative to said frusto-conical masking surface, said rst leg portion being longer than said second leg portion and closer to said axis;

and means including separate members respectively lcoupled to the extremities of said leg portions for applying said ring member to said interior surface -of said envelope to compress said masking surface of said bight portion against said interior envelope surface through-out said predetermined circumferential larea with a greater contact pressure at said leading edge than at said trailing edge, and for rst pivoting said ring member inwardly toward said axis .and then withdrawing said ring member paraxially from said envelope after the application of said coating.

References Cited bythe Examiner FOREIGN PATENTS 557,047 5/1957 Belgium.

MORRIS KAPLAN, Primary Examiner. 

1. APPARATUS FOR USE IN THE APPLICATION OF A CONDUCTIVE COATING TO THE INTERIOR SURFACE OF A CATHODE-RAY TUBE ENVELOPE COMPRISING: A BIFURCATED MEMBER OF RESILIENT MATERIAL COMPRISING A PAIR OF DIVERGENT LEG PORTIONS CONNECTED BY A BIGHT PORTION HAVING LEADING AND TRAILING EDGES AND ADAPTED FOR CONTACTING SAID SURFACE THROUGHOUT A PREDETERMINED AREA THEREOF; AND MEANS FOR APPLYING SAID BIGHT PORTION TO SAID SURFACE WHILE DIFFERENTIALLY STRESSING SAID LEG PORTIONS TO COMPRESS SAID BIGHT PORTION AGAINST SAID SURFACE THROUGHOUT SAID PREDETERMINED AREA WITH A GREATER CONTACT PRESSURE AT SAID LEADING EDGE THAN AT SAID TRAILING EDGE. 